1. Field of the Invention
The present invention relates to medical devices. Specifically, the invention relates to a device for removing blood clots or thrombi from body vessels, such as the small arteries associated with the brain.
2. Description of Related Art
Mechanical thrombectomy is a procedure that has been in widespread use for many years. Typical thrombectomy devices are balloons that are inflated in a vessel and then withdrawn to pull clots into a sheath which can be withdrawn from the patient to remove the clots. Other devices are simple open ended catheters into which a clot is aspirated and removed from the patient. Another thrombectomy device employs a basket device that is opened within the clot so that the clot becomes captured in the basket. The basket can then be retrieved along with the clot. Still other devices use a small corkscrew shaped device that is collapsed inside a catheter. The catheter is passed through the clot, the corkscrew is pushed out of the catheter allowing the device to expand, capturing the clot for removal. Some corkscrew devices are simply “screwed” into the clot, then retracted into a catheter for removal before the corkscrew is retracted.
All of these devices may, however, have certain disadvantages. For example, the balloon catheter devices are first advanced through the clot before they can be inflated and retracted. The process of penetrating the clot with the balloon catheter device tends to push the clot deeper into the arterial circulation where it becomes even more difficult to remove. This issue also occurs with basket and corkscrew devices that are collapsed into an outer delivery sheath and passed through the clot before they can be deployed and retracted. The action of pushing a device through the center of the clot pushes the clot deeper into the artery and sometimes fragments the clot, making it into an even more dangerous embolus. The corkscrew devices that are screwed into the clot usually have a smooth rounded tip to prevent the corkscrew from penetrating the vessel wall or otherwise damaging the vessel wall as it is screwed into the clot. With these devices, however, the smooth, rounded central tip does not screw into the clot, but instead is pushed into the clot and then the remainder of the corkscrew is screwed into the clot. This results in a pushing force on the center of the clot and a pulling force on the periphery of the clot. These counter forces tend to macerate or fragment the clot and result in only a small part of the clot being captured. Some corkscrew devices may substitute a sharp tip that can screw directly into the clot for the rounded tip. However, sharp tips can penetrate the vessel wall just as easily as they can penetrate and capture the clot. Such devices are seldom used since they carry the very high risk of penetrating the vessel wall. When a bead or ball is applied to the tip of the device that is large enough to protect the vessel wall, it will be so large that it will tend to push the clot distally rather than penetrate the clot such that the clot can be captured and removed.
Another issue associated with conventional thrombectomy devices is that they are typically too large and too stiff for use in the small tortuous vessels of the brain. Also, many conventional devices use a central mandrel, wire, or some other structure for support. These support structures will also displace clots, making it difficult to capture all the clot material.
Still another issue includes capturing any of the loose fragments possibly dislodged from the clot during removal of the clot. Another issue arises if a thrombectomy device has a diameter smaller than the vessel diameter when deployed from the catheter. In such a case, some of the clot immediately adjacent the vessel wall may not be removed.
In view of the above, it is apparent that there exists a need for an improved mechanical thrombectomy device.